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Machine Creation Services (MCS) Storage Optimization (MCSIO), is a new feature within MCS provisioning and was introduced in XenApp and XenDesktop 7.9.

MCSIO reduces I/O load through a two-tier caching system. An in-memory cache, known as the “temporary memory cache,” is used as the first storage tier. If the in-memory cache fills up, subsequent writes will be cached using an additional disk attached to the provisioned machine as the second tier - this is known as the “temporary disk cache.” To achieve this, MCSIO provisioned machines have an additional MCSIO driver to intercept and manage IO operations.

For improved I/O performance, both the storage tiers should be adequately sized, so that the likelihood of writes directly reaching the system disk reduces considerably. If the caches are not sized right, then they may soon run out of space for writes, causing the driver to direct writes to the system disk. This in turn will reduce cache hits, increase direct disk accesses, and thus, significantly degrade I/O performance. To avoid this, administrators should continuously monitor the I/O load on the MCSIO driver, understand how the driver uses the in-memory and disk cache for managing these I/O operations, and make sure that the caches are sized right to support these operations. This is where the CtxXcXAMCSSDTest test helps!

This test tracks the I/O requests to the driver and reports the rate at which the driver reads from or writes into each of the caches and he system disks in order to process these requests. This way, the test reveals whether/not the caches are doing a good job of preventing direct disk accesses. Additionally, the test also closely monitors how the memory in the in-memory cache and the disk space in the cached disk is utilized, and proactively alerts administrators to any potential resource crunch in the caches. This way, the test provides useful sizing pointers to administrators.

Measurement	Description	Measurement Unit	Interpretation
Cache_disk_data_read	Indicates the rate at which data is read from the cache disk.	KB/Sec
Cache_disk_data_write	Indicates the rate at which data is written to the cache disk.	KB/Sec	A steady drop in the value of this measure could indicate a writing bottleneck. One of the reasons for this could be the lack of enough disk space in the cache disk. Check the value of the Cache disk utilization measure to determine whether/not there is a space crunch.
Cache_disk_data_rw	Indicates the rate at which data is written to and read from the cache disk.	KB/Sec	A steady drop in the value of this measure is indicative of an I/O bottleneck.
Cache_disk_read	Indicates the rate at which read operations are performed on the cache disk.	Reads/Sec
Cache_disk_write	Indicates the rate at which write operations are performed on the cache disk.	Writes/Sec
Cache_disk_iops	Indicates the rate at which read and write operations are performed on the cache disk.	Operations/Sec
Cache_disk_size	Indicates the current size of the cache disk.	MB
Cache_disk_used	Indicates the amount of space that the driver has used in the cache disk.	MB
Cache_disks_free	Indicates the amount of space that is unused in the cache disk.	MB
Cache_disk_util	Indicates the percentage of space used in the cache disk.	Percent	A value close to 100% is a cause for concern as it indicates that the cache disk is running out of disk space. You may want to expand the capacity of the cache disk to make sure that the writes do not spill over to the system disks.
Cache_mem_data_read	Indicates the rate at which data is read from the in-memory cache.	KB/Sec
Cache_mem_data_write	Indicates the rate at which data is written to the in-memory cache.	KB/Sec	A steady drop in the value of this measure could indicate a writing bottleneck. One of the reasons for this could be the lack of enough memory. Check the value of the Cache memory utilization measure to determine whether/not there is a memory crunch.
Cache_mem_data_rw	Indicates the rate at which data is written to and read from the in-memory cache.	KB/Sec	A steady drop in the value of this measure is indicative of an I/O bottleneck.
Cache_mem_read	Indicates the rate at which read operations are performed on the in-memory cache.	Reads/Sec
Cache_mem_write	Indicates the rate at which write operations are performed on the in-memory cache.	Writes/Sec
Cache_mem_iops	Indicates the rate at which read and write operations are performed on the in-memory cache.	Operations/Sec
Cache_mem_target_size	Indicates the amount of memory that the MCS storage driver will aim to use.	MB
Cache_mem_used	Indicates the amount of memory that the driver has actually used.	MB
Cache_mem_free	Indicates the amount of memory that is unused.	MB
Cache_mem_util	Indicates the percentage of memory that the driver has utilized.	Percent	A value close to 100% is a cause for concern as it indicates that the in-memory cache is rapidly running out of memory. You may want to allocate more RAM to the cache to make sure that the writes do not spill over to the cache disk.
Storge_driver_read_req	Indicates the number of read requests that were received by the MCS storage driver since boot.	Number
Stroge_driver_write_req	Indicates the number of write requests that were received by the MCS storage driver since boot.	Number
Storge_driver_rw_req	Indicates the number of read and write requests that were received by the MCS storage driver since boot.	Number	This is a good indicator of the I/O load on the driver.
Sys_disk_data_read	Indicates the rate at which data is read from the system disks.	KB/Sec
Sys_disk_data_write	Indicates the rate at which data is written to the system disks.	KB/Sec
Sys_disk_data_rw	Indicates the rate at which data is written to and read from the system disks.	KB/Sec
Sys_disk_reads	Indicates the rate at which reads are performed from the system disks.	Reads/Sec
Sys_disk_writes	Indicates the rate at which writes are performed into the system disks.	Writes/Sec
Sys_disk_iops	Indicates the rate at which I/O operations are performed on system disks.	Operations/Sec	A zero value is desired for this measure.